1. Field of the Invention
The present invention relates generally to injection molding apparatuses for heating and slurrying an ingot or metal material, and each time a predetermined amount of the slurried material is accumulated in an injection port of an injecting machine, injecting the slurried material into a mold to form a desired metal molded article.
More particularly, the present invention relates to an improved injection molding apparatus which constantly permits forming of good-quality molded articles by performing control such that an uniform amount of the slurried material can always be injected into the mold.
The present invention also relates to an improved injection molding apparatus which can greatly simplify the arrangements required for detecting whether or not there is an ingot in a heated-ingot receiving chamber provided upstream of ingot crushers and for supplying inert gas into the receiving chamber, and which also permits reliable detection of presence or absence of an ingot in the receiving chamber as well as reliable and smooth supply of inert gas into the receiving chamber.
2. Description of the Related Art
In Japanese Patent Laid-Open Publication No. HEI 5-285625, the assignee of the present invention proposes an injection molding apparatus for manufacturing metal molded articles, which is designed to increase productivity by heating and slurring an ingot, i.e., material to be molded, in successive operations as will be outlined below with reference to FIG. 9.
FIG. 9 is a vertical sectional view schematically showing the proposed injection molding apparatus 100, which generally comprises a screw-type injecting machine 101 including a screw shaft 111 rotatable and axially movable within a machine cylinder and having a spiral groove along a predetermined length thereof, and a material feeder section 102. The material feeder section 102 includes, in the top-to-bottom direction of the figure, an ingot entry 103, ingot heating chamber 104 provided with an inductive heater, and crushed material accumulating chamber 107 having rotary cutters 106. The accumulating chamber 107 is connected in communication with the heating chamber 104 via a heated-ingot receiving chamber 105. The interior of the entire material feeder section 102 is maintained in a vacuum or inert gas atmosphere, and the above-mentioned chambers 103, 104 and 105 are partitioned off by sliding shutters 108 and 109.
In the proposed injection molding apparatus 100, an ingot 110, such as an Mg alloy ingot, fed via the ingot entry 103 is heated in the heating chamber 104 into a half-molten condition and passed through the chamber 105 to the crushing/accumulating chamber 107 to be crushed by the rotary cutters 106. Then, the crushed material is fed to the injecting machine 101, where it is agitated and kneaded into slurry by rotation of the screw shaft 111 and temporarily accumulated, as a final slurried material to be molded, in an injection port formed between the fore ends of the machine cylinder and screw shaft 111. Each time the slurried material has been accumulated to a predetermined amount necessary for forming a desired metal molded article, it is directly or indirectly injected through a nozzle into a cavity 113 of a metal mold 112 by injecting action of the screw shaft 111.
However, the material tends to be crushed into non-uniform sizes and thus the crushed material tends to be fed from the cutters 106 to the injecting machine 101 in non-uniform amounts, particularly because the crushing and feeding rate of the crushed material depends on the operating rate of the cutters 106 being intermittently driven. Consequently, the slurried material would often be injected, in an amount short of the predetermined amount, from the injection port of the machine 101 into the mold 112, with the result that proper molded articles could often not be formed. If the cutters 106 are constantly driven in order to avoid the above-mentioned problem, the crushed material may be overfed to the injecting machine 101 and excessively accumulated up to the cutters located upstream of the injecting machine 101. As a result, the excessively accumulated crushed pieces will thrust in between the cutters 106, thus seriously damaging the cutters 106.
Further, in the molding apparatus 100, if the heated ingot 110 is not properly fed from the receiving chamber 105 to the cutters 106, the cutters 106 may run idle resulting in no crushed material being supplied to the injecting machine 101. Such an idle condition is undesirable from the viewpoint of efficiency of the injection molding apparatus. Therefore, when supply of the heated ingot 110 to the cutters 106 is interrupted for some reason, a next ingot must be immediately supplied via the receiving chamber 105 to the cutters 106. Besides, the ingot must be fed to the cutters 106 smoothly and reliably. To this end, it is necessary to reliably detect whether there is a heated ingot received in the receiving chamber 105 so that a next ingot can be immediately fed to the receiving chamber when no ingot is received therein.
Further, in order to prevent unwanted oxidation of the ingot, the receiving chamber 105, etc. must be maintained in an inert gas atmosphere. Besides, the receiving chamber 105 has a limited height just sufficient to vertically receive the heated ingot to be crushed by the cutters 106. But, in the prior art molding apparatus 100, the arrangements for detecting presence or absence of an ingot in the heated-ingot receiving chamber 105 and supplying inert gas into the receiving chamber 105 are provided completely separately in the chamber 105, and they require a large space and too many parts. Further, because such parts are attached directly to the wall surface of the receiving chamber, a number of steps are required to make the receiving chamber itself.